A color luminance meter for measuring a luminance (Lv) and a chromaticity (x, y) of a liquid crystal monitor is configured by equipping it, for example, with a measuring probe disposed opposed to a display screen of the liquid crystal monitor, and a main meter unit. The measuring probe is operable to measure, for example, tristimulus values of X, Y, Z color-matching functions defined by the CIE (International Commission on Illumination), by respective sensors, and the main meter unit is operable, based on a result of the measurement, to calculate a luminance and a chromaticity of the display screen as a measuring object.
A typical conventional technique related to a measuring optical system for use in such a color luminance meter or a colorimeter is disclosed, for example, in the following Patent Document 1.
In the Patent Document 1, a bundle fiber is employed to introduce incident light into three colorimetric optical systems corresponding to respective ones of the tristimulus values. Each of the colorimetric optical systems is configured by combining a color filter corresponding to a respective one of the tristimulus values, with a light-receiving sensor, wherein each of the color filters of the colorimetric optical systems is disposed at a respective one of three branched exit end of the bundle fiber. The bundle fiber of the Patent Document 1 is circumferentially divided into six groups as viewed from the side of an circularly-bundled inlet end, wherein each pair of diagonally located ones of the groups are bundled together. This facilitates the mitigation of measurement errors resulting from directivity (luminous intensity distribution characteristic).
However, each of the color filters is configured by laminating a plurality of optical absorption filters in such a manner as to transmit incident light at a transmittance corresponding to a respective one of a plurality of desired spectral characteristics such as the tristimulus values X, Y, Z, so that there is a problem that it is impossible to design a filter having a characteristic with transmittance peaks in two wavelength bands, as illustrated, for example, in FIG. 21, in other words, design freedom or flexibility is limited. There is another problem of low transmittance and large light intensity loss. Particularly, in a film-shaped color filter, there is yet another problem of severe aged deterioration due to (poor stability against) heat, light (ultraviolet light), temperature, etc.
Therefore, a conventional technique intended to employ, as each of the color filters, an interference type filter (hereinafter referred to as “interference filter”) in place of the optical absorption filter is proposed, for example, in the following Patent Document 2. This interference filter is configured by laminating several tens of dielectric layers or oxide layers on a glass substrate through vacuum deposition, spattering or other process, and operable to select a transmission/reflection wavelength by the action of optical interference.
However, in the interference filter, a transmittance thereof varies depending on incident angles. Thus, there is a problem that, in the case of 0-degree incidence of parallel light, error sensitivity is high.